1. Technical Field of the Invention
The present invention relates to ribbon feed systems for matrix printers.
2. Description Regarding the Art
Matrix-type ribbon printers present special ribbon feed problems particularly when the printing process requires uninterrupted electrical contact between the printhead and the ribbon. For such printing, the ribbon has typically been laid out along the print line and the printhead then scans the ribbon. By first laying out fresh ribbon along the print line, ribbon motion relative to the receiving medium, which would tend to cause smearing, is avoided.
U.S. Pat. No. 4,195,937 describes a number of ribbon feed configurations. All of the configurations use supply and takeup reels located off the printhead carrier, an arrangement that complicates ribbon loading and threading. Prior to a printing scan along the print line, the ribbon is clamped in place. For one configuration, a barlike clamp serves to collect printing current. And, for most of the configurations described, the operator must look to the pattern on the ribbon to inspect the material printed on the present print line. One of the configurations does route the ribbon to permit viewing of the print line with the ribbon clamped in place. Printing current for this configuration is collected by a conducting bar and/or a roller that redirects the ribbon from the print line.
U.S. Pat. No. 3,855,448 describes, for one implementation, an on-carrier ribbon feed, but it appears that intermittant printhead contact is intended rather than a sweeping movement. Indeed, with the drive described, the ribbon would tend to move relative to the receiving medium unless the printhead carrier is at a standstill. Also, the type of printhead described does not involve the complication to ribbon feeding of collecting printing currents from the ribbon.